Homebuilt—Swallow 2

Jan 04, 2011 4 Comments by

The inspiration for this model came from a recent article in the April 2010 issue of our sister publication FLIGHT JOURNAL. The full-size aircraft originated in Germany in 1927 known as the Klemm L.25. In the early 1930s this same basic plane, ended up in Great Britain as the British Aircraft Company’s “Swallow 2”. It reminded me of the popular PT-19 U.S. Army Air Force military trainer. Its high-aspect-ratio wing practically made the aircraft a powered glider and I thought it would also make a perfect RC sport/trainer aircraft.

            I first built a micro version with 75 square inches that weighed only 2.1 ounces which appeared in the May 2010 issue of RC Micro World. For this construction article I built a larger version intended for electric powered park flying. It has 175 square inches of wing area and should weigh in at about 12 ounces maximum. Input power was selected at about 50 watts yielding a power loading of approx. 70 watts per pound. It is a simple to build sport scale and it retains the same basic shape of the aircraft and required about a week to build.


 

 

 

The subject of this construction article is this 175 square inch version of the British Aircraft Company SWALLOW-2. It is an electric powered park flyer size aircraft weighing 12.1 ounces.

 
Another view of the two SWALLOW-2 models, the smaller size weighs 2.1 ounces while the larger park flyer weighs 12.1 ounces. Both are electric powered!

 

Pictured at the left is an already published micro version of the SWALLOW-2. This plane has 75 square inches of wing area and weighs only 2.1 ounces. The article appeared in the May 2010 issue of RC MICRO WORLD.

 

A rear quarter view of the SWALLOW-2. This park flyer falls into the category of “fantasy scale or “sport scale”. Considerably more scale detail could be added if you like!

 

Let’s start building

The basic wing structure is built-up open framework with ribs along with a pair of barn door, scale-like ailerons. Cutouts are made in the underside of the wing to accept two aileron servos, (one per aileron.) Each servo is held in place with double-sided tape. Extension leads are required to connect the aileron servos to the receiver located inside the fuselage. The center wing section is flat and the outer wing panels are attached to it to produce the dihedral. The wing is removable with the help of two screws and a length of dowel.

The main landing gear requires some wire bending, cutting and silver soldering. This may look complicated, but will prove much easier than you might think. The tail surfaces are made from medium to hard 1/16-inch balsa. Notice that cross-grained reinforcement inserts were added to strengthen the tail surfaces. The fuselage consists of medium to hard 1/16-balsa sides. The upper portion of the fuselage is like a turtle deck made from soft 1/16-inch balsa. This will take a little extra time, but adds a lot to the scale appearance.

            The full-size aircraft had a radial engine with exposed cylinder heads. I chose not to add this detail to save some time. But you could fashion a dummy engine using the end of a plastic bottle with the cylinder heads fashioned from scrap balsa. Two dummy exhaust pipes can be made from simple soda straws.


 

This particular wing design has a flat center section in addition to the two outer panels.


 

 

The underside of the wing center section showing the plywood strips to which the landing gear wires are attached later on.

 

 

The wing now fully assembles (outer panels attached to the center section). Plywood braces are used at the dihedral joints. The ailerons are added later after covering the wing.

 

 

A closer look at the main landing gear which is made up from .055 inch diameter wire with a rear brace wire made from .047 inch diameter wire. The two wires are bound with soft copper wire and then silver soldered. Both wires are attached to the plywood strips with pieces of thin scrap aluminum and sheet metal screws.

 

 

The aileron servos are both attached to 1/16 balsa “floors” with double sided tape. Both aileron servos are separately plugged into the receiver. A “Y” connector is not used in this application.

 

Radio Gear

The airplane is a 4-channel design with controls for ailerons, elevator, rudder and throttle. The aileron servos were separately connected to the receiver with “Flaperon” function enabled on my Spektrum DX-7 transmitter. This allowed me to adjust the positions of both ailerons and even raise them slightly for a bit of washout effect. In total four S60 Sub-micro servos were used.

 

Final Assembly

            For power I chose a BP Hobbies Gold 2204-19 brushless outrunner motor turning an APC 8×3.8  Slo-Fly prop. This provides input power of about. 53 watts using a 2-cell FMA CellPro 1300mAh Li-Po pack (an alternate 800mAh pack made the plane somewhat tail heavy!) A Jeti Advance 8 amp brushless ESC handled the motor and includes a BEC so that only one battery pack is required. At the final weight of 12.1 ounces, the power loading worked out to 70 watts per pound.

            The entire plane was finished with two types of iron-on covering. The outer wing panels and all tail surfaces were covered with BP Hobbies opaque white Solite. The fuselage and wing center section were covered in Military or Insignia blue Monokote. The wingwalks and simulated cockpits were cut from a black contact shelving paper. The windshields were fashioned from 0.015-inch-thick clear Acetate. I made my own decals using  Desktop Publishing Supplies decal paper. The lettering was done on my computer with MS Word and then I inkjet printed my decals onto the adhesive backed paper. Conclusion

My smaller indoor flyer version of the Swallow 2 was a big success and as it turned out this larger park flyer version is a total success in every regard. It flies great, is easy to build and cover, doesn’t cost very much compared to sport ARFs from the hobbyshop and the comments it receives at my local flyer field made the project totally worthwhile!

 


 

The fuselage stars with the two 1/16 inch balsa sides with bracing strips made from 1/8 square balsa. A doubler is also employed by the wing saddle.

 

Support triangles hold the fuselage sides in position as the assembly begins. This is done using the top view of the fuselage. Crosspieces are fashioned from 1/8 square balsa.

 
Cross pieces all in place as the fuselage takes on it’s final shape.

 
Two stringers go on top of the formers, and then 1/16 balsa sheeting is added.

 
Fuselage top is now fully sheeted and sanded. A little Spackle helps at this point.

 

IN THE AIR

With the final CG Location at 1 3/8 inch back from the leading edge (using a 2.9 ounces, 2S 1300mAh Li-Poly battery,) flying the Swallow 2 proved just great! At full power the model climbs out with total authority! For cruising I was able to come back to almost half throttle, which made the flying really comfortable and greatly extended flight time upwards of 15 minutes! Winds of 10 mph can be handled with ease.

Basic maneuvers like loops and rolls are also possible. I did not use any dual rate or expo rate control on this model. It just wasn’t necessary!         The one thing I did observe was that when slowing down for a landing, there was a slight amount of  tip stalling. This was a little surprising since the CG is rather far forward. But just
to be safe I re-heated the wing covering and added a bit of wingtip washout, (raised the trailing edge.) I suspect this results for the relatively high aspect ratio wing. In the final plans I show the wing trailing edge raised about 1/8 inch at the beginning of the ailerons. Building in the washout during construction is much preferred. The Swallolw 2 is just a perfect flying aircraft, great for any sport pilot, even a novice flyer!

 

Control Throws:

Ailerons: +-1/4 inch

Elevator: +- 1/2 inch

Rudder: +-1 inch

 

SPECIFICATIONS

Model:             Swallow 2

Type:               Sport scale electric park flyer

Wingspan:       39 inches

Wing Area:      175 square inches

Weight:           12.1 ounces

Wing Loading: 9.9 oz/sq.ft.

Length:            24 inches

 

GEAR USED:

Radio: Spektrum DX-7 transmitter; Spektrum 6-channel receiver, 4 E-Flite S60 Sub-Micro servos; 2 12-inch servo extension leads.

Motor: BP Hobbies Gold 2204-19 brushless outrunner

ESC: Hobby Lobby Jeti Advance 8 amp (w/BEC)

Prop: APC 8×3.8 SloFly

Battery: FMA Direct 1300mAh CellPro Li-po


 

Battery compartment is at the lower, front of the fuselage, directly behind the firewall. The pack is held in place with Velcro tape.

 

This is the complete power and RC system that goes into the SWALLOW-2. Total weight was 117.6 grams (4.15 ounces). The receiver is a Spektrum AR6110, which weighs only 3.5 grams.

 
The rudder and elevator servos are located in the wing area of the fuselage. Stevens Aero Models .078 inch yellow Teflon tubes carry the .032-inch diameter control rods back to the control surfaces at the rear end of the fuselage. These tubes should be anchored every few inches to prevent flexing or buckling as the controls are operated.

 
Stab and vertical fin have now been attached to the fuselage. In this photos you can see the control rod attached to the rudder.

 

BP Hobbies Gold 2204-19 brushless outrunner motor is reliable, yet very inexpensive. Prop is an APC 8 X 3.8 SloFly type.


 

The upper portion of the wing center section showing how the two aileron extension cables exit the wing. They in-turn plug into the aileron and Auxiliary port on the receiver. By enabling the flaperon function each aileron servo can be separately adjusted.

 

An overall view of the forward underside showing the landing gear and battery pack, with the wing mounted in place.

 

These are the decals that Bob made up using the adhesive backed decal paper available from Desktop Publishing Supplies Inc. The letters are created on Microsoft WORD then ink jet printed to the special paper.

 

An overall view of the SWALLOW-2 underside.

 

 

Elevator connection and the DuBro micro tail wheel bracket (No. 854).

A dummy radial engine might be added for more scale detail. Cockpits and wing walk strips were fashioned from black contact shelving paper. Windshields were made from .015 inch Acetate.

 
 

MANUFACTURERS

BP Hobbies CA medium and thin viscosity cement, five-minute epoxy cement, brushless outrunner motor and Solite iron-on covering.

www.bphobbies.com

DuBro Products (micro control horns, micro EZ-Connectors, lightweight wheels and wheel collars,)

http://www.dubro.com/

FMA Direct (2 cell CellPro 1300 mAh Li-Poly battery pack)

www.fmadirect.com

Hobby Lobby International (Jeti Advance 8 amp ESC)

www.hobby-lobby.com

Horizon Hobby (Spektrum AR6110 receiver, DX-7 transmitter and four E-Flite S60 servos) http://www.horizonhobby.com/Products/Default.aspx?ProdID=EFLB0990
Stevens Aero Models (.073 Yellow Teflon Tubing for elevator control rod)

http://www.stevensaero.com/shop/product.php?productid=16639

 
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4 Responses to “Homebuilt—Swallow 2”

  1. David W Choate says:

    I am currently building this plane. the build is simple, but I wish they had better pictures of the w-1 dihedral mount. Am I supposed to cut it in half, or slot the wing?

  2. David W Choate says:

    I bought your plan. i’m building the plane. What is the best way to make the right side wing panel as it is not on the plan. I made a copy to cut out for templates, and traced over the left side wing panel with a light under so I could see the lines,but there must be a better way.

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